Lift trucks



Nov. 10, 1959 Filed Deb. 22, 1955 A. E. R. ARNOT LIFT TRUCKS 2 Sheets-Sheet 1 Nov. 10, 1959 A. E. R. ARNOT 2,911,793

LIFT TRUCKS Filed Dec. 22, 1955 I 2 Sheets-Sheet 2 United States Patent LIFT TRUCKS Alfred Erwin Reginald Arnot, Basingstoke, England, as-

signor to John Reginald Sharp and Emmanuel Kaye, Basingstoke, Hampshire, England Application December 22, 1955, Serial No. 554,813

Claims priority, application GreatBritain December 24, 1954 I 5 Claims. (Cl. 60-97) This invention comprises improvements in or relating to lift trucks.

I -The invention relates particularly to trucks of the type which have power-operated gear for for holding, lifting and releasing a load as desired. -It is an object of the invention to provide means which prevent loads from being released while being held by the gear in lifted position, and so dropped and damaged.

According to the present invention, in a truck of the type described, the lifting means are of the type which requires a constant application of a force to keep the load in the lifted position, and such force is utilized to operate a device which acts to prevent release of the holding means as long as the said lifting force is being applied.

For example the load may be lifted by hydraulic pressure and the source of hydraulic pressure which is applied to keep the load in the lifted position may be connected to a pressure-operated device which acts to prevent release of the load. Where the gear for holding and releasing the load is hydraulically operated, the pressure operated device must act to prevent release of the hydraulic holding pressure. This may be direct, that is to say the pressure operated device may ensure that pressure cannot be released from the holding device as long as pressure is applied to the lifting device, or it may act through electrical contacts in the case where electromagnetically controlled valves are used for the hydraulic circuit. In the later case it is sufficient for a pressure switch to be used on the lifting circuit which operates interlock contacts in the electrical control circuit of the releasing valves.

The following is a description by way of example of one construction in accordance with the invention:

In the accompanying drawings,

Figure 1 is a diagram of a part of a truck and of hydraulic control connections thereon, the truck being viewed in plan; and

Figure 2 is a similar view of combined electric and hydraulic control connections.

Referring to Figure l, the truck is supposed to comprise a horizontal chassis 11 having wheels 12 at the front end and a mast comprising channel-shaped members 13 in which is mounted a vertically movable carriage 14. The carriage can be raised and lowered by means of a hydraulic motor 15 and it carries clamp arms 16 adapted to grip a load 51 and capable of being closed together upon the load by operation of a hydraulic motor comprising a cylinder 17 attached to one arm and a piston and ram 18 attached to the other. The chassis 11 of the truck extends rearwardly and horizontally and carries a steering wheel or wheels at the rear end, all these parts being well known and therefore not requiring further description.

The chassis 11 is indicated to a larger scale in chain "ice line at 11a and carries an internal combustion engine 20 for driving the truck, which is also employed for driving an hydraulic pump 21 which draws through a suction pipe 22 from a reservoir 23 and delivers to two delivery pipes 24, 25.

The pipe 24 delivers pressure fluid to a valve 26 whence the fluid is conveyed by pipes 27, 28, to the hydraulic motor 15 for raising and lowering the carirage 14. The control valve 26 may be of any desired construction and is indicated as comprising an upper pressure chamber 29 to which the pipe 24 is connected. Below this is a distribution chamber 30 out ofwhich the pipe 27 issues and into which pressure fluidmay be admitted by a lift valve 31 in a partition 32. Below the partition 32 there is a second partition 33 and the space below this is connected by a pipe 34 to the reservoir 23. Exhaust to the reservoir 23 is controlled by a lift valve 35 and the lift valves 31, 35 are operated by a lever 36 in the exhaust chamber below the partition 33 mounted on a rock shaft which is operable by a control handle 37. Rocking the handle 37 to the right as viewed in the drawing, lifts the valve 31 and admits pressure fluid to the pipes 27, 28, to extend the hydraulic motor 15 and raise the carriage .14. Rocking the control lever 37 to the left, as viewed in the figure, closes the valve 31 and opens the valve 35 permitting the pressure fluid to escape from the hydraulic motor 15 through the valve 35 and exhaust pipe 34 so that the carriage 14 is lowered. A flow control valve may be used to restrict the lowering movement of the carirage in known manner.

The delivery pipe 25 goes to a two-part valve 40 which controls the operations of the hydraulic motor 17. The valve 40 is shown in the drawing in the form of a diagrammatic perspective with the two sections of the valve separated from one another so as to be clearly seen and each section is similar to the valve 26 already described, that is to say it comprises upper pressure chamber '41, an intermediate distribution chamber 42 and a lower exhaust chamber '43 which latter contains an operating lever 44 in each case. The operating levers 44 are mounted upon a rock shaft 45 which is common to them and is actuated by a hand-lever 46 corresponding to the lever 37 of the Valve 26. There are lift valves 47 which control admission of pressure fluid from the chambers i 41 to the distribution chambers 42 and there are other lift valves 48 which control the connections to exhaust. The lift valve 47 of one section is on the opposite side of its operating lever 44 from that of the corresponding valve of the other section and therefore moving the operating lever '46 in one direction admits pressure to one of the chambers 42 and exhausts the other'charnber 42 in the other section of the valve, while rocking the lever 46 in the other direction reverses the operation. A pipe 50 from one section of the valve leads to one end of the hydraulic motor cylinder 17 and operates the hydraulic motor in a direction for opening the clamps 16. From the distributionchamber 42 of the other section of the valve'there extends a pipe 54 leading to another pipe 55 which 'is connected to the other end of the cylinder 17 and serves to close the clamp arms 16 upon the load 51. Thus the clampingarrns can be closed or opened by rocking the control lever 46 in one direction or the other. A relief valve 52 is provided on a branch 53 from the. pipe 54 so that the clamping pressure on the load can be limited and preferably the relief valve 52 isadjustable to suit the character of the load.

An interlock valve 56 is provided which contains. a chamber 57 connected between the pipes. 27 and 28. In this chamber is 'a piston 58 operating against a spring 59. The piston 58 has formed solidly therewith a piston valve 60 which is connected between the pipes 54, 55, and is such that when there is no pressure or a predetermined pressure in the pipes 27, 28, a condition which corresponds to the carriage 14 being lowered so that the load 51 is resting on the ground or on some support or when the carriage is being .raised or lowered without a load in the clamps, thepassa'ge through the pipes 54, 55 is opened by the piston valve 60. In this condition the clamps 16 can be opened or closed by the control lever 46. As soon however, as pressure is applied by the control lever 37 to the pipes 27, 28, the piston 58 is forced over and the connection between pipes 54, 55, is closed. Under these conditions the pressure in the cyl inder {17 holding the clamps in closed position is maintained and they remain closed gripping the load as long as the load is lifted.

Referring now to Figure 2, this shows the same principle applied to an electrically-controlled truck. The diagram Figure 2 is laid out on the same principle as Figure l and the parts of the truck which correspond to Figure 1 are similarly numbered. The description of these parts will therefore not be repeated. In the present case however, a truck chassis 'llcarries an electric battery 61 which is connected by a line 62 to a motor 63 driving a pump 64 which delivers by pipe 65 to the pipe 27 before described. A control switch 66 is provided having a handle 67 which, if moved to the left as shown in the figure, closes a switch arm 68 on to a contact 69 which is in series with the motor 63 and the circuit line 70 is thereby connected between the motor 63 and the other end of the battery 61 so that the motor is started and the pump 64 operated to raise the carriage 14. If the control handle 67 is moved in the other direction another switch arm 71 closes a contact 72 on a line 73 going to an electromagnetic winding 74 of an electromagnetic valve 75 in a bypass pipe 76 on the pump delivery 65. Moving the handle to the right energizes the electro-magnetic winding 74 and opens the by-pass. The motor 63 and pump 64 are stopped at the same time. Theresult is that the pipe 27 is connected to the reservoir 23 and the carriage 14 is lowered. A non-return valve may be arranged in the delivery pipe 65 and a flow control valve may be arranged in the pipe 76 to restrict the lowering movement of the carriage.

In a similar way a line 77 from the battery is connected to an electric motor 78 driving another pump 79. The pump delivery 79 is to a pipe 80 which goes to a solenoid control valve 81. The valve 81 comprises a piston valve member 82 which is normally forced to the right, as viewed in the figure, by a spring 83 but can be moved to the left when so required by solenoid winding 84. In the normal position shown in the figure the valve 82 is urged to the right by the spring 83 and the pressure connection is open to a pipe 85 which leads to the closing end of the hydraulic motor cylinder 17 so that the clamps 16 are normally closed upon the load when the pump 79 is operating. Another pipe 86 extends from the valve 81 to the opening end of the hydraulic motor cylinder 17 and there are exhaust connections 87 from the valve 81 to the reservoir 23. If the solenoid winding 84 is energized it moves the valve member 82 to the left as shown in the drawing and thereby closes the connection of the pipe 85 to the pressure and opens it to the exhaust connection 87, while opening the pipe 86 to pressure and closing the connection of this pipe to exhaust. will therefore serve to open the clamp 16 if the pump 79. is working. A control switch 88 having a control handle 89 and a switch arm 90 is provided and the control switch 88 is arranged with a contact 91 connected to the solenoid winding 84 by a line 92. The other end of the solenoid winding is connected by a line 93 through contacts 94 hereinafter described to a line 95 leading to one pole of the battery 61. The switch arm 90 is connected Energizing the winding 84 by a line 96 to the other .pole of the battery. Moving the lever 89 to the left therefore as viewed in the drawing will energize the solenoid winding 84 and operate the valve member 82 to connect. the pipe 86 to pressure and open the clamp. This circuit however is only complete through the contacts 94 when there is no pressure in the pipes 27, 28, and the piston 58 of the interlock valve 56, which in this case is adapted to operate the contacts 94 has been urged to the left by the spring 59. Therefore the clamp cannot be opened when pressure is being applied to the lifting motor 15 to raise the load.

The switch 88 is also provided with other contacts 97, 98, on a line 99 running to a motor-starting contactor 100 having -a solenoid winding 101 connected to the line 99 and thence by a line 102 to the contacts 94. The result is that the motor 78 is started (by closure of contacts 103, 104 of switch 100 which are in a line 105 leading to the motor 78) whichever way the lever 89 is rocked, provided the contacts 94 are closed, that is to say provided that the load is not being lifted. Thus, rocking the lever 89to'the right will close the clamping members if the motor cylinder 15 is not being raised or lowered or is not under pressure in its raised position.

The lever 89 is further provided with contacts 106 connected by a line 107 to an electromagnetic valve 108 which is opened when the lever is rocked in either direction. The effect of the valve 108 is to lock the motor '17, 18 in any position to which it has been moved by the application of pressure to clamp the load but to unlock it at the same time as the motor 78 is started either to open or close the clamping members. The valve 108 is also connected to the contacts 94 so that when pressure is being applied to the cylinder 15 the valve cannot be released and the pressure in the cylinder 17 is maintained to clamp the load 51 while it is raised. As before there is a relief valve 52 on the pipe (which corresponds to the pipe 54 of Figure 1) to limit the clamping pressure.

I claim:

.1. A fluid pressure-operated system comprising in combination a first fluid system, a second fluid system, a pressure-operated device in communication with and responsive to pressure in said first fluid system, an electromagnetically controlled isolating valve in said second fluid system and operative connections between said valve and said pressure-operated device which operative connections include electrical contacts on the pressure-operated device interlocked with the electromagnetic control of the valve to actuate the isolating valve to hold pressure in said second system when said first system is under pressure.

2. In a lifting device, the combination of a hydraulic lifting cylinder-and-piston element, a hydraulic pressure supply connection thereto, a control valve for said supply, a lifting device lifted by said lifting cylinder-and-piston element, hydraulically operated load holding means on said lifting device, a second hydraulic supply connection thereto to cause it to hold a load, a second control valve for said second supply, an isolating valve in said second supply, a pressure-operated interlock connected to the supply to the lifting device so as to be operated whenever said lifting device is energized to lift the load, and means operated by said interlock when so energized to ensure that the isolating valve is operated to trap hydraulic fluid pressure in said load holding means.

' 3. A lifting device as claimed in claim 2 wherein the hydraulic isolating valve is electromagnetically operated and the pressure operated interlock carries electrical contacts to operate the isolating valve.

4. A lifting device as claimed in claim 3 wherein the pressure-operated interlock also serves to cut off said second supply of hydraulic pressure when the isolating valve is closed.

5. A lifting device as claimed in claim -4 wherein the second supply of hydraulic pressure is effected by an electrically driven pump and the pressure-operated inter- 5 6 lock serves to disconnect the driving motor of said pump 2,676,463 Klessig Apr. 27, 1954 when pressure is in supply to the lifting cylinder. 2,682,150 Ballinger June 29, 1954 2,693,084 Badger Nov. 2, 1954 References Cited in the file of this patent 2 732 0 3 Smith 24, 1956 UNITED STATES PATENTS 5 2,795,346 Farmer ne 11, 1957 2,363,179 Harrington et a1 Nov. 21, 1944 FOREIGN PATENTS 2,500,933 Dalley 5 723,857 Great Britain Dec. 15, 1953 2,571,550 Ehmann Oct. 16, 1951 

